Phased Array Radar Antennas are described in chapter 7 of The Radar Handbook, edited by Merrill Skolnik, published by McGraw-Hill Publishing Co. (2d ed. 1990), and herein incorporated by reference. As written by S. M. Sherman, published by Artech House (1984), and in Monopulse Radar, by A. I. Leonov and K. I. Fomichev, published by Artech House, Inc. (1988), both of which are herein incorporated by reference, monopulse processing for a planar antenna array for radar typically involves the synthesis of sum and delta beams, as is well-known for a rectangular antenna aperture. For a rectangular aperture the beams may also be separable in azimuth and elevation, which is desirable for advanced electronic counter-counter measures (ECCM) while preserving the monopulse ratio, as described in "Combining Sidelobe Canceller and Mainlobe Canceller for Adaptive Monopulse Radar Processing," patent application Serial No. 07/807,548, filed Dec. 16, 1991, by Yu et al., "Adaptive Digital Beamforming Architecture and Algorithm for Nulling Mainlobe and Multiple Sidelobe Radar Jammers While Preserving Monopulse Ratio Angle Estimation Accuracy," patent application Ser. No. 07/807,546 (RD-19,509), filed Dec. 16, 1991, by Yu et al., and "Simultaneous Sidelobe and Mainlobe Radar Jamming Canceller for Adaptive Monopulse Processing," patent application Ser. No. 07/912,398 (RD-21,283), filed Jul. 13, 1992, by Yu et al., all assigned to the assignee of the present invention and herein incorporated by reference. Presently, various circular antenna apertures are available for use in radar systems. Examples of such apertures are described in chapter 5 of The Antenna Handbook, edited by Y. T. Lo and S. W. Lee, and published by Van Nostrand Reinhold Co. (1988). A need exists for an antenna beamformer specifically for use with such circular antenna apertures.